1. Field of the Invention
The invention relates to a light guiding plate. More particularly, the invention provides a light guiding plate used in a vertical backlight module of a liquid crystal display, a scanner or an advertisement panel.
2. Description of the Related Art
Display devices play an important role in communicating information through images. A CRT-type display device uses an electron beam to display images on a curved or flat panel. A picture tube of the CRT-type display device occupies a substantially large space to provide the necessary electron beam. A principal disadvantage of the CRT display therefore is the space occupied thereby.
Recently, a compact display device such as a liquid crystal flat display has been developed and put into production. It has become popular due to its low weight and space saving advantages. Laptop computers are consequently made increasingly thinner and more compact by employment of liquid crystal displays, to facilitate transportation thereof. Increasingly, desktop computers are also equipped with liquid crystal display devices since the price of the liquid crystal display devices has dropped. Space reduction of the display device brings the user a comfort of use and allows him/her to fully utilize the working space.
The optical module assembled with a light guiding plate realizes the flattening of the display device. Referring to FIG. 1, a conventional vertical backlight module 9 includes a base 90, a reflector 91, an illumination element 92, a light guiding plate 93, a diffusion plate 94 and a liquid crystal module 95. The base 90 is a rectangular solid and has a curved inner surface 96 to attach to the arc-like reflector 91. The illumination element 92 is mounted in an approximately central location of the base 90 and above the reflector 91. Opposite sides of the rectangular light guiding plate 93 are respectively fastened to a surface 96 of the base 90. The rectangular diffusion plate 94 is also fastened to the surface 96 and attached on the light guiding plate 93. Then, the liquid crystal module 95 is attached on the diffusion plate 94. Thereby, a conventional vertical backlight module 9 is accomplished.
In the above structure of the conventional backlight module 9 (as shown in FIG. 2), light irradiated from a lower part of the illumination element 92 and reflected by the reflector 91 is transmitted to the light guiding plate 93. Light irradiated from an upper part of the illumination element 92 is guided directly to the light guiding plate 93 without reflection. In particular, the light irradiated right from the top of the illumination element 92 is transmitted directly to the light guiding plate with the shortest transmission distance. Since the light guiding plate 93 is flat, all the incident light is guided to the diffusion plate 94 at a constant angle. The distribution of the incident light in the diffusion plate 94 is the same as that of emergent light from the light guiding plate 93. Therefore, the light intensity at the area right above the illumination element 92 of the backlight module 9 is substantially higher than that at other areas. This causes an uneven light emergence on the whole display of the backlight module 9. As a result, the glow of the vertical backlight module 9 is adversely affected.